The invention relates to a method for the recovery of a video signal.
Video signals which are transmitted via a channel are, as a rule, influenced by the channel characteristics. This applies, in particular, to channels which are susceptible to interference, such as the terrestrial transmission of TV signals. Signal interference may occur due to ambient influences on the transmission path.
There is thus an interest in compensating for this interference in the receiver and in obtaining an optimal reproduction quality.
In the case where the channel characteristics are known in the receiver, interference can be eliminated by means of suitable compensation measures, such as e.g. an equalizer. However, knowledge of the channel characteristics is not provided e.g. in the case of terrestrial transmission. In order to ensure interference-free reception even in the case of such transmission channels which are subject to interference, an adaptive equalizer can be used. It is then necessary, however, to transmit a reference signal with the useful signal, from which reference signal the corresponding compensation parameters are then derived by the adaptive equalizer. For capacity reasons, however, such reference signals are not prescribed by the transmitter.
The invention is based on the object of specifying a method for the recovery of a video signal which, without an additional reference signal, to the greatest possible extent eliminates channel interference which influences the quality of the video signal.
According to the invention, an adaptive equalizer is used which is trained by the digital data signals, such as e.g. teletext data, that are concomitantly transmitted in a video signal.
An adaptive equalizer adapts itself independently in order to compensate for unknown or time-variable channel characteristics. An input signal which is interfered with by the channel is changed by the adaptive equalizer until a desired output signal is present. Since adaptive equalizers cannot judge when a desired analogue output signal is present given an analogue input signal, the digital data signal that is concomitantly transmitted with the analogue input signal is advantageously used for the adjustment of the adaptive equalizer.
It is preferable for the adaptive equalizer to be adapted to the optimal reception condition during the transmission duration of the digital data signals and for this adjustment then to be maintained during the transmission duration of the analogue signals.